                1. Field of the Invention        
The invention relates to a device for creating and conveying a gas-powder mixture, in particular for coating processes such as cold-gas spraying, at an increased pressure, in accordance with the preamble of claim 1.                2. Discussion of Background Information        
As is known, cold-gas spraying is a spraying technique for metals and plastics materials, in which a powdered spraying material consisting of metal, metal alloys or plastics material is sprayed onto a substrate at high speed, in particular supersonic speed, in such a way that because of the high kinetic energy thereof, the powder bonds with the material of the substrate. The gas, preferably nitrogen, is accelerated to supersonic speed by high pressure and by means of a de Laval nozzle (Venturi nozzle).
Heating the gas jet increases the flow speed of the gas and thus also the particle speed. The heating of the particles which also occurs in this connection promotes the deformation thereof on impact. However, in cold-gas spraying the gas temperature is considerably less than the melting point of the spraying material, and so the particles in the gas jet do not melt.
A device of this type is known for example from EP 0 484 533 A1. This document uses a powder container in which a metering drum arranged at the base meters powder into a downstream mixing chamber, into which the gas is introduced at high pressure. Subsequently, the mixture is accelerated to the desired supersonic speed in a supersonic nozzle. The powder container, metering drum and mixing chamber are located in a single housing, where the powder holding chamber is further connected via a gas pressure compensation line to the gas supply line so as to distribute the pressure evenly in the powder holding chamber and in the mixing chamber and to eliminate the effect of pressure on the metering of the powder. However, this known device is of a relatively complicated construction, is expensive to manufacture and has relatively large dimensions.